MR imaging is known to be an effective technique for the noninvasive diagnosis of thoracic aortic disease, but it has not been used to monitor the appearance of the aorta or the fate of the false lumen after surgery for aortic dissection. This study describes our initial experience with postsurgical MR imaging of aortic dissection (nine type A and two type B) to evaluate prognostically important features, including the status of residual false lumen. The most notable findings were (1) aneurysmal dilatation beyond the interposed graft (11/11 cases), (2) residual intimal flap (10/11 cases) with at least partial patency of the false lumen (10/10 cases), and (3) origin of a visceral vessel from the false lumen in persistently dissected abdominal aorta (6/9 cases). Evaluation of residual false lumen by double-spin-echo-intensity and phase-display techniques showed evidence of slow blood flow with variable amounts of thrombus in eight of 10 cases. Differentiation between signal within the false lumen due to slow flow and signal due to thrombus was facilitated by phase display. MR imaging can be used for noninvasive monitoring of the aorta after surgical repair of aortic dissection. Since the false lumen usually remains patent after surgical repair, such follow-up of its status seems necessary for identifying potential complications of the original dissection and/or the therapy.